From Ketosis to Autophagy: My 5-Day Fast
- Apr 17
- 5 min read
I Was Wrong. I Admit It.
The first time it happened was in the late 1990s. A work colleague mentioned she was doing a three-day fast — something she did every few months. Fasting went against everything I had learned while preparing for my health coach certification exam. I had been taught that grazing — eating small meals throughout the day — was essential for keeping metabolism steady. Going without food for days, I believed, would cause the body to store more calories as fat once normal eating resumed.
Although I may have made a face, I think (and hope) I kept my opinions to myself. Still, part of me was curious. Could I go three days without eating? Thankfully, I thought at the time, I would never need to find out.
Years later, another colleague told me he only ate two meals a day — lunch and dinner. I scoffed. “Breakfast is the most important meal of the day,” I assured him. Yet I couldn’t help noticing that he lost a healthy amount of weight and kept it off.
Was I misinformed?
It turns out the answer was yes.
About seven years ago, I began working out first thing in the morning. Because my body doesn’t respond well to eating after exercise, I started delaying my first meal until noon or later. Breakfast may be the most important meal of the day — but that doesn’t necessarily mean we need to eat it first thing in the morning.
Today, I practice what is known as time-restricted eating (TRE), a form of intermittent fasting. There are many variations, but my day is divided into an eight-hour eating window followed by sixteen hours of not eating. Some people divide the week into five normal eating days and two fasting days. Rather than harming my metabolism, TRE feels surprisingly natural. Before food was constantly available, our ancestors regularly went for periods of time without eating.
First Stop: Ketosis
Carbohydrates are the body’s preferred fuel source. Most of the time, your body burns glucose made from the carbohydrates in your last meal. If you burn through that glucose before eating again, your body turns to reserves stored in the liver as glycogen. When glycogen stores are depleted, the body begins converting fat into ketones for fuel.
This fat-burning state, called ketosis, typically begins 12–24 hours after your last meal, depending on activity level, glycogen stores, and how accustomed your body is to fasting.
Reported benefits of ketosis include weight loss without loss of lean muscle, improved mental clarity, appetite suppression, better blood sugar regulation, reduced insulin resistance, and decreased inflammation. Research also suggests ketosis may benefit people with epilepsy and type 2 diabetes.
Fasting is not the only way to enter ketosis. A diet high in fat and low in carbohydrates can trigger it as well. While the keto diet remains popular, the quality of macronutrients matters. Are we choosing unsaturated fats like avocados and walnuts, or relying heavily on saturated fats such as red meat and bacon? Severely limiting carbohydrates can also reduce intake of fiber-rich fruits and vegetables. Over time, this may disrupt gut microbes and potentially increase the risk of depression. Although the keto diet has passionate supporters, the long-term effects of maintaining ketosis through diet remain unclear.
Autophagy: The Body’s Deep Clean
Ketosis is often described as a layover on the journey to autophagy — a deeper state of cellular cleansing that typically occurs after 24–72 hours of fasting.
Our bodies perform routine housekeeping every day. Autophagy, however, is more like an intensive spring cleaning. Cells sweep up and recycle damaged components, much like vacuuming under sofa cushions reveals lost treasures and spare change.
Potential benefits include improved immune function, removal of cellular debris associated with neurodegenerative diseases such as Alzheimer’s and Parkinson’s, DNA repair, stem-cell regeneration, reduced inflammation, and improved cholesterol and triglyceride levels.
Fasting is not recommended for children, adolescents, older adults, pregnant or breastfeeding individuals, people with a history of eating disorders, or anyone taking prescription medications without medical supervision. Risks may include bone loss, low blood pressure, slowed healing, irritability, and depression. Always consult your physician before beginning a fasting protocol.
From Curiosity to Commitment
For years I’ve been intrigued by the idea of inducing autophagy, but the thought of going without food for days felt intimidating. About a year ago, I learned about fast-mimicking diets (FMDs) — structured eating plans that provide minimal food while still encouraging the body to enter a fasting state. Allowing small amounts of food can make longer fasts more manageable and sustainable. Studies in mice suggest periodic fasting using FMDs may increase lifespan and support cognitive function.
Understanding the science shifted my perspective. Fasting began to feel less like deprivation and more like a biological rhythm the body already understands. Across cultures and spiritual traditions, fasting has long been used as a doorway to clarity and renewal.
So, with the support of an FMD, I’ve finally worked up the courage to see what happens.
My 5-Day Fasting Experiment
I’m embarking on a five-day fast beginning Sunday, April 19. Based on my research, I can expect fatigue and flu-like symptoms by day two as my body transitions into fat-burning mode. Day three may be the most intense. I’ll be documenting the experience through daily video updates.
When I think about our hunter-gatherer ancestors, it seems unlikely they ate every day. Autophagy may be nature’s way of helping the body adapt to cycles of feast and famine. Three robust meals a day appears to be a relatively modern convention.
Years ago, I easily transitioned to two meals a day. It’s possible my body already dips into ketosis more often than I realize. I love and respect my body, so if this challenge feels harmful rather than healing, I will stop.
But I’m curious.
Maybe I’ll complete all five days. Maybe I’ll discover something unexpected. Maybe I’ll decide to repeat the experience in a few months.
I’ll be sharing the journey as it unfolds. Stay tuned — and wish me luck. ✨
P.S. Our understanding of nutrition is constantly evolving. That’s why I believe it’s important to rely on trustworthy sources and remain open to new discoveries. For more information, check out How to Make Sense of Contradictory Nutrition Claims.
References
Jamal Rahmani, et al. “The influence of fasting and energy restricting diets on IGF-1 levels in humans: A systematic review and meta-analysis.” Ageing Research Reviews, Volume 53, 2019. https://doi.org/10.1016/j.arr.2019.100910.
Ocean Robbins. “Intermittent Fasting 101: A Guide to its Health Benefits & Risks.” Food Revolution Network. July 10, 2020. https://foodrevolution.org/blog/intermittent-fasting-101/
Wei, Min et al. “Fasting-mimicking diet and markers/risk factors for aging, diabetes, cancer, and cardiovascular disease.” Science translational medicine vol. 9,377 (2017): eaai8700. doi:10.1126/scitranslmed.aai8700
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